Smooth transition and ripple reduction in 4-switch non-inverting buck-boost power converter for WCDMA RF power amplifier

In this paper, smooth transition between Buck and Boost modes in 4-switch non-inverting Buck-Boost power converter is investigated. It is shown, both theoretically and on an experimental converter prototype, how pulse-width modulator (PWM) maximum and minimum duty cycle limitations can result in pulse skipping at the mode transition and substantial increases in the output voltage ripple. This is a very significant problem when the converter is used as a power supply for WCDMA RF power amplifiers. An approach is proposed to achieve smooth mode transition by overlapping Buck and Boost modes of operation. The approach results in much reduced output voltage ripple, at the expense of reduced efficiency, as demonstrated on the experimental prototype.